1. Field of the Invention
The present invention relates to optical property measuring apparatus and optical property measuring method, exposure method and exposure apparatus, and device manufacturing method, and more particularly to an optical property measuring apparatus that receives a light via an optical system to be examined with a detector and measures optical properties of the optical system to be examined and an optical property measuring method, an exposure apparatus that comprises the optical property measuring apparatus and an exposure method that utilizes the optical property measuring method, and a device manufacturing method in which the exposure apparatus and the exposure method are used.
2. Description of the Related Art
Conventionally, an exposure apparatus that transfers a pattern formed on a mask or reticle (hereinafter generally referred to as ‘reticle’) onto an object such as a wafer coated with resist and the like or onto a glass plate (hereinafter referred to as ‘wafer’ as appropriate) via a projection optical system has been used in a lithographic process for manufacturing semiconductor devices, liquid-crystal displays and the like. As this type of exposure apparatus, in recent years, from the viewpoint of emphasizing the importance of throughput, projection exposure apparatus of a sequentially moving type are mainly used, such as the reduction projection exposure apparatus by the step-and-repeat method (the so-called stepper), and the scanning projection exposure apparatus by the step-and-scan method that is an improvement of the stepper.
In this type of exposure apparatus, it is important to accurately overlay and transfer a reduced image of a pattern of a reticle onto a shot area that has been already formed on the wafer. Therefore, it is required to adjust optical properties of a projection optical system and an illumination optical system so that a forming state of an image by the projection optical system becomes a desired state.
Thus, for the adjustment of optical properties described above, it is premised that the optical properties of optical systems such as the projection optical system are measured with good precision. For example, as image-forming characteristics of the projection optical system, conventionally, low-order aberrations that are known as Seidel's five aberrations were measured based on the exposure results of an image of a measurement pattern or the measurement results of an aerial image of the measurement pattern. In recent years, however, in order to cope with a finer device pattern according to higher integration of a semiconductor device, measurement of wavefront aberration that is a total aberration as the image-forming characteristics of the projection optical system has been relatively often performed.
The wavefront aberration of the projection optical system slightly changes before and after the projection optical system is installed into the body of the exposure apparatus. Therefore, various measuring units that measure the wavefront aberration of the projection optical system in the so-called on-body state (i.e. a state installed into the body of the exposure apparatus) are used. As one of this type of measuring units, a wavefront aberration measuring instrument by the Shack-Hartmann method using a microlens array is known.
A measurement principle of the wavefront aberration using the wavefront aberration measuring instrument is as follows. More specifically, a spherical wave generated from a pinhole formed on a reticle enters a projection optical system, and the light via the projection optical system enters the wavefront aberration measuring instrument fixed to a wafer stage. Then, a wavefront of the light at a pupil plane of the projection optical system is divided by a microlens array arranged in the vicinity of a plane conjugate with the pupil plane of the projection optical system, and an image of the pinhole (a spot image) is formed on an imaging plane of a CCD by each lens element making up the microlens array. In this case, the wavefront aberration of the projection optical system can be calculated by performing a predetermined computation based on a position deviation of each spot image from a datum point.
In order to accurately obtain the position deviation of each spot image from the datum point, it is required to measure a position and a shape of the pupil plane of the projection optical system, and a wavefront aberration measuring instrument having the following configuration is also known (e.g. refer to Patent Document 1): a half mirror is arranged inside the wavefront aberration measuring instrument, the light incident on the wavefront aberration measuring instrument is branched by the half mirror, and one branched beam enters a CCD via the microlens array and the other branched beam enters another CCD (a CCD for pupil measurement) without passing though the microlens array.
The half mirror has the following polarization properties. More particularly, the light reflecting off the half mirror has a high intensity of S polarization and a low intensity of P polarization, while the light passing through the half mirror has a low intensity of S polarization and a high intensity of P polarization. As a matter of course, there are slight differences in polarization properties depending on the material of a semi-transmissive film (reflective film having transmittance that is not zero) to be used for the half mirror, however, it is difficult to manufacture a semi-transmissive film having no polarization properties.
Meanwhile, with the projection exposure apparatus, it is likely that the aberration of the projection optical system (a projection lens) is different depending on a polarization direction, or it is also likely that an illumination light is polarized.
Therefore, with the wavefront aberration measuring instrument disclosed in Patent Document 1 described above, measurement precision could be deteriorated due to the polarization properties existing in the half mirror described above.
Besides the wavefront aberration measuring instrument by the Shack-Hartmann method described above, as a device to measure the wavefront aberration of the projection optical system, various interferometers (such as a Twyman-Green interferometer, a shearing interferometer, and a point diffraction interferometer) are also known. However, because most of these interferometers have a half mirror, the measurement precision could be deteriorated likewise, due to the polarization properties existing in the half mirror.
Patent Document 1: Kokai (Japanese Unexamined Patent Application Publication) No. 2003-262948.